Design of Interaction Region Gang Xu Accelerator Physics Group IHEP, Beijing, Oct. 14, 2001

Content Introduction to BEPCII Requirements to IR design from accelerator physics Detector boundary condition IR beam line layout IR Magnets Background and consideration of new design Summary

Introduction to BEPCII 2-ring collider— factory type machine Synchrotron radiation facility Basic parameters (next page)

Introduction to BEPCII(continued) Tab. 1 Main parameters Energy E(GeV) 1.55 Energy spread(10-4) 4.23 Circumference C(m) 237.53 Emittance εx/εy(μm) 0.21/0.003 Energy loss/turn U0(keV) 55.8 Momentum compact α 0.036 RF frequency frf(MHz) 499.8 β*x /β*y(m) 1/0.015 RF Voltage Vrf(MV) 1.5 Chromaticity ξx/ξy 13.3/28.5 Total current/beam I(A) 1.116 Tunes νx/νy/νz 6.64/7.58/0.047 Particle number Nt 5.51×1012 Crossing angle θx(mrad) ±11 SR Power P(kW) 62.3 Bunch spacing Sb(m) 2.4 Bunch number Nb 93 Damping time τx/τy/τz(ms) 44/44/22 Bunch current Ib(mA) 12 Beam-beam parameter 0.04/0.04 Bunch length σz(cm) Luminosity(1033cm-2s-1) 1.0 Natural bunch length σz0(cm) 1.1 Effective impedance() 0.7

Requirements to IR design from accelerator physics Rapidly separate the beams into two rings Squeeze the vertical beta function to 1.5cm Compensate the coupling from detector solenoid Connect the two outer rings to provide the synchrotron radiation Keep the background in the acceptable level All accelerator components in IR must stay in the space limited by the detector HOM heating due to the mask and the discontinuity of vacuum chamber should be considered

Boundary condition Detector geometric condition

Boundary condition(continued) Summary of the main geometric conditions The first accelerator component must be after 0.5m away from IP Before 1.15m, the outer aperture of components must be less than Φ384mm Before 1.9m, the outer aperture of components must be less than Φ756mm

Boundary condition(continued) Detector solenoid(Bs=1T, new design value 1.2T)

Boundary condition(continued) Aperture of IR vacuum chamber(Half ) For collision beam 1. 14σx+xoffset+10mm c.o.d.(εx=0.25μm) 2. 14 σy+5mm c.o.d. (full coupling εy=0.125μm) For injection beam 3. 16σx+xoffset+3mm c.o.d. For SR photons(collision beam) 4. Out of the trajectories of SR photons from 10 σ particles

IR beam line layout Crossing angle θx(mrad)=±11 relative to the detector solenoid axis Beam comes to IP from outer ring then goes into inner ring 1st S.C. magnet has combined anti-solenoid(ASOL) and bending coil(SCB), the latter is used in synchrotron radiation mode Both electron and positron are off the axis of SCQ All S.C. coils are in one cryostat ISPB is a septum type magnet, it will bend the beam in inner ring OQ1, IQ1, OQ2, IQ2 are special magnets with dual aperture, beam goes through their axes.

IR beam line layout(continued) βy max<120m(βy *=1.5cm)180m(βy *=1cm), βx max<6m in s=0~1.9m

IR Magnets(Superconducting) Anti-solenoid ASOL with integral strength 1.42 T·m, 0.6m away from IP, it will be extended onto SCQ to cancel the effect of the solenoid fringe field SCB placed at the same location as ASOL with integral strength 0.26 T·m SCQ with strength 17.6T/m and effective length 0.4m, 1.15m away from IP

IR special magnets(Normal) D to IP (m) L D between e± BSC(H×V) strength entry exit (mm) ISPB 2.25 0.4 78 108 72×72 90×64 0.6T OQ1 2.90 131 167 101×59 106×58 12T/m IQ1 3.55 0.5 190 235 129×47 136×42 OQ2 4.55 281 326 82×72 78×73 IQ2 5.55 372 417 106×38 101×35

Background issue and consideration of new design Since the beam coming from outer ring is off axis in the SCQ, this will lead to synchrotron radiation. From the previous plot, the minimum distance between beryllium pipe and the trajectory of the photon is only 7.2mm. This situation must be improved.

7.2

Three improvement methods Increase the radius of the beryllium pipe Add a bending coil on SCQ to cancel(or partially) the bending field due to the off axis for the beam in outer ring, this will lead to BSC increasing from Φ120 to Φ140 Place SCQ to the center of outer ring beam orbit, this will lead to the equivalent BSC increasing from Φ120 to Φ170

Before doing the improvement, we need to know What is the acceptable level of the synchrotron radiation? The more detail boundary conditions in IR The acceptable heating power of each IR component

Summary IR design is very preliminary Due to the background issues we must do more detail IR design Many items are not taken into account such as background from the loss particle, vacuum, beam diagnostics, …